The long-term objectives of the proposed research are to: 1. Characterize the various mechanisms for electron reactions catalyzed by flavoproteins. 2. Obtain evidence regading the effect of the protein environment on flavin reactivity and the catalytic function of active site amino acid residues. 3. Evaluate the role of the coenzyme in those flavoenzymes where catalysis does not involve oxidation-reduction. Studies related to the latter objective will seek to determine the structure of the flavin derivative in yeast DNA photolyase and to evaluate the hypothesis that the coenzyme functions as a photosensitizer in the catalytic reaction. Studies with glycolate oxidase and lactate oxidase will seek to obtain unambiguous evidence for substrate dehydrogenation via a carbanion intermediate and to identify the active site base. Studies with sarcosine oxidase will focus on the cataly tic function and properties of its two nonequivalent flavins and will seek to determine whether 1-electron steps are involved in substrate dehydrogenation or in interflavin electron transfer. Evidence regarding coenzyme environment and reactivity will be sought in studies involving reaction of peroxides with enzyme-bound 5-deazaflavin. The propoed research will involve kinetic and structural analysis and will include reactions with normal substrates, substrate analogues, inhibitors and modified flavin derivatives. Mechanism studies may contribute to the development of a specific inhibitor for glycolate oxidase or a synthetic catalyst for the DNA photolyase reaction which could be of therapeutic significance in treating primary hyperoxaluria or certain forms of xeroderma pigmentosum, respectively.